Carbon nanocomposite sorbent and methods of using the same for separation of one or more materials from a gas stream

ABSTRACT

The present invention relates to carbon nanocomposite sorbents. The present invention provides carbon nanocomposite sorbents, methods for making the same, and methods for separation of a pollutant from a gas that includes that pollutant. Various embodiments provide a method for reducing the mercury content of a mercury-containing gas.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support awarded by the U.S.Department of Energy (DOE) under DOE Cooperative Agreement NumberDE-FC26-08NT43291 entitled “EERC-DOE Joint Program on Research andDevelopment for Fossil Energy-Related Resources”; Subtask 4.8 entitled“Fate and Control of Mercury and Trace Elements”; EERC Fund Number14990. The government has certain rights in this invention.

BACKGROUND OF THE INVENTION

Mercury (Hg) emissions have become a health and environmental concernbecause of their toxicity and ability to bioaccumulate. The U.S.Environmental Protection Agency (EPA) has issued regulations for thecontrol of Hg emissions from waste-to-energy, cement production, andcoal-fired power plants. Mercury in flue gas from industrial sources(e.g., power plants) can be captured by injection of sorbents such asactivated carbon, which can then be removed by particulate collectiondevices. The amount of standard sorbents (e.g., activated carbon) neededto serve the market is large. Standard sorbents are not always effectiveand become more expensive as injection rates increase.

A nanocomposite is a multiphase solid material in which one of thephases has at least one dimension of less than about 1000 nm or in whichless than an about 1000 nm repeat distance separates the phases thatmake up the material. Nanocomposites in which one or more of the phasesis a bulk matrix and one or more other materials is a nanodimensionalphase can have unique properties, with the mechanical, electrical,thermal, optical, chemical, or catalytic properties of the nanocompositematerial differing significantly from that of the individual componentmaterials.

The first examples of carbon nanocomposites were prepared byintercalating monomers into interlamellar spaces in clays, polymerizingthe monomer, and carbonizing the polymer. The minimum thickness of thecarbon layer was 1.1 nm (Kyotani—1988). In the next two decades, avariety of monomers were employed with several clays and other poroussupport materials. In some cases, the inorganic part of the compositewas removed to study the graphite-like carbon structures. In 2004,Bakandritsas et al. produced carbon-clay nanocomposites using sucrose asthe carbon source (Bakandritsas—2004). The thickness of each layer wasabout 1 nm and 0.4 nm for the clay and graphene layers, respectively.Later, this group described the use of these for adsorption of gases(CO₂, CH₄, N₂) and organic solutes in aqueous solutions(Bakandritsas—2005). Because they can be easily shaped, have highsurface-areas, and conduct electricity, carbon-clay nanocomposites fromsucrose were used to produce electrodes and sensors (Darder—2005,Gomez-Aviles—2007, Fernandez-Saavedra—2008, Gomez-Aviles—2010). Theporous carbon-clay nanocomposites from sucrose also have been utilizedfor catalyst supports (Nguyen-Thanh—2006a. Nguyen-Thanh—2006b,Ikeue—2008).

Several applications of composite materials for adsorption of metal ionssuch as Hg²⁺ have been described in the literature. These include thefollowing materials: chitosan-coated ceramic (Boddu—2002), polypyrrolefilm on clay (Eisazadeh—2007), mercapto-functionalized polysiloxane filmon diatoms (Wang-2007), polyaniline film on ash (Ghorbani—2011), andpolyaniline composite with humic acid (Zhang). None of these is a carbonnanocomposite; rather, they are typically a polymer film deposited on asupport and suffer limitations from stability and difficulty ofrecycling and processing.

Separation of elemental or oxidized mercury from a gas stream has beenconducted with several types of nanocomposites made with non-carbonmaterials. A SiO₂—TiO₂ nanocomposite was used for Hg capture under UVradiation (Li—2008). This technology suffers from the difficulty ofhaving to effectively irradiate combustion effluent containing fineparticulate. A magnetite- and Ag-impregnated zeolite nanocomposite wasdescribed (Dong—2009). It is suspected that the Ag nanocompositerepresents a significant environment risk in itself, as well as being ahigh-cost sorbent. Capture of Hg in flue gas with a CeO₂—WO₃/TiO₂nanocomposite was reported (Wan—2011). These non-carbon sorbents havehigher cost and slower kinetics than desirable.

SUMMARY OF THE INVENTION

In various embodiments, the present invention provides a method forseparating a material from a gas that includes the material. In someembodiments, the material can be a pollutant or an unwanted constituentof the gas. The method includes providing or obtaining a carbonnanocomposite sorbent. The method also includes contacting at least someof the material with the sorbent to form a material-sorbent composition.The method also includes separating at least some of thematerial-sorbent composition from the material-containing gas. Theseparation gives a separated or partially separated gas.

In various embodiments, the present invention provides a method forreducing the pollutant content of a pollutant-containing gas. The methodincludes providing or obtaining a carbon nanocomposite sorbent. Themethod includes providing or obtaining a halogen or halide promoter. Themethod includes promoting at least a portion of the sorbent material.The promoting of the sorbent material includes chemically reacting theportion of the sorbent material with the halogen or halide promoter. Thepromoting of the sorbent material gives a promoted sorbent. The methodincludes contacting at least part of the promoted sorbent with thepollutant. In some embodiments, the method can also include contactingthe pollutant with sorbent that is unpromoted. Contacting the promotedsorbent with the pollutant forms a pollutant-sorbent composition. Themethod also includes separating at least some of the pollutant-sorbentcomposition. The separation gives a cleaned gas, having a lowerpollutant content than the starting material (e.g., uncleaned)pollutant-containing gas. In various embodiments, the pollutant can bemercury.

In various embodiments, the present invention provides a method offorming a carbon nanocomposite material. The method includes obtainingor providing a carbon precursor material. The method includes providingor obtaining a substrate material. The method includes contacting thecarbon precursor and the substrate material to provide a nanocompositestarting material. The method also includes heating the nanocompositestarting material to provide the carbon nanocomposite sorbent. Invarious embodiments, the present invention provides the carbonnanocomposite that is generated by the method. In some examples, thepresent invention provides the nanocomposite in combination with variousmaterials the nanocomposite encounters during performance of the method,such as the nanocomposite in combination with mercury, with oxidizedmercury, or with a mercury-containing gas. In some embodiments, themethod can include adding a halogen or halide promoter and allowing thepromoter to react with the sorbent to form a promoted carbonnanocomposite sorbent.

Surprisingly, despite activated carbons being routinely used to capturepollutants in flue gas streams, carbon nanocomposites have not been usedbefore for gas-phase mercury capture. Traditional thinking is that anexcess of inorganic support such as clay in the carbon nanocompositehinders the sorption of the pollutant on the carbon. However,surprisingly, in accord with some embodiments of the present invention,the non-carbon parts can enhance the sorption of pollutant on theproximate carbon graphene layer. The basal planes of the carbon portionsof the nanocomposites are indeed largely hindered within carbonnanocomposite structures. However, the carbon edge structures are verywell exposed in the structures, and these are the part of the carbonthat is active for pollutant capture (e.g., mercury, selenium, arsenic,and the like). As described herein, the graphene edge structures can bepromoted by reaction with a halogen, hydrogen halide, or ammonium halideto produce a carbocation edge structure that is highly reactive foroxidation and capture of pollutants such as mercury.

Since support materials such as clays are by themselves inert, thepromotion of oxidation of pollutants by the carbon layer caused bycertain support materials is also unexpected. However, in accord withsome embodiments of the present invention, a polyanionic aluminosilicatelayer (e.g., from clay) can stabilize the development of cationic siteson the proximate graphene carbon structures that are essential foroxidation of pollutants such as mercury. The same stabilizing effect canoccur with a carbon-diatom (silicate) nanocomposite or othernanocomposites composed of graphene layers and polar inorganicstructures.

In embodiments that include a nanocomposite that is promoted viahydrogen halide compound obtained from degradation or reaction of thecorresponding ammonium halide, another advantageous role for theinorganic portion can be in providing a binding site for the ammoniathat is released from either the decomposition or reaction of theammonium salt. The bound ammonia forms a complex with basic characterthat reacts with SO₂ in the flue gas and prevents their interferencewith the capture on the edge structure of pollutants such as mercury.

In another advantage of inorganic support in embodiments that includeclay as the support, the clay is stabilized to dispersion in an aqueousmedium. Clays are usually difficult to filter or separate from anaqueous medium, but in the form of a nanocomposite with carbon, thematerial can be easily separated from an aqueous medium by filtration.Thus, the nanocomposite can be conveniently utilized to capture mercuryin an aqueous environment.

The present invention advantageously can separate a material (e.g., apollutant) from a gas that includes that material more efficiently thanother methods. The present invention provides certain advantages overother methods and materials for the removal of mercury frommercury-containing gas. The method and materials of various embodimentsof the present invention can capture and remove mercury from a gas moreefficiently than other methods of mercury removal. The method andmaterials of various embodiments of the present invention can operatemore efficiently than other methods of mercury removal. For example, themethod and materials of various embodiments can remove a given amount ofmercury for a smaller amount of financial expenditure, as compared toother methods. For example, the method and materials of variousembodiments can remove a larger amount of mercury for a given mass ofcarbon, as compared to other methods of removing mercury, including ascompared to other methods of removing mercury that include a carbonsorbent. Thus, the method and materials of various embodiments canresult in the use of less sorbent material (e.g., less carbon overall),as well as the disposal of less used sorbent material, than othermethods of mercury removal.

In various embodiments, the present invention provides a method forreducing the mercury content of a mercury-containing gas. The methodincludes providing or obtaining a carbon nanocomposite sorbent. Thecarbon nanocomposite sorbent is made by steps including providing orobtaining a carbon precursor and providing or obtaining a substratematerial. The steps also include contacting the carbon precursor and thesubstrate material. The contacting provides a nanocomposite startingmaterial. The steps also include heating the nanocomposite startingmaterial. The heating provides the carbon nanocomposite sorbent. Themethod for reducing mercury content of the mercury-containing gas alsoincludes providing or obtaining a halogen or halide promoter. The methodincludes promoting at least a portion of the sorbent material. Thepromoting of the sorbent material includes chemically reacting theportion of the sorbent material with the halogen or halide promoter. Thepromoting of the sorbent material gives a promoted sorbent. The methodincludes contacting at least part of the promoted sorbent with themercury. Contacting the promoted sorbent with the mercury forms amercury-sorbent composition. The method also includes separating atleast some of the mercury-sorbent composition from the gas. Theseparation gives a cleaned gas, having a lower mercury content than theuncleaned gas.

In various embodiments, the present invention provides a method ofmaking a carbon nanocomposite sorbent. The method includes providing orobtaining a carbon precursor. The method includes providing or obtaininga substrate material. The method includes contacting the carbonprecursor and the substrate material. Contacting the carbon precursorand the substrate material provides a nanocomposite starting material.The method also includes heating the nanocomposite starting material.Heating the nanocomposite starting material provides the carbonnanocomposite sorbent.

BRIEF DESCRIPTION OF THE FIGURES

In the drawings, which are not necessarily drawn to scale, like numeralsdescribe substantially similar components throughout the several views.Like numerals having different letter suffixes represent differentinstances of substantially similar components. The drawings illustrategenerally, by way of example, but not by way of limitation, variousembodiments discussed in the present document.

FIG. 1 schematically illustrates methods for preparation of promotedcarbon sorbents, in accordance with various embodiments.

FIG. 2 illustrates a proposed mechanistic model of the chemicalreactions resulting in the oxidation and capture of mercury, inaccordance with various embodiments.

FIGS. 3A and 3B schematically illustrate preparation of promoted carbonsorbents and processes for flue gas mercury reduction in flue gases(e.g. from combustion) and/or product gases from a gasification system,in accordance with various embodiments.

FIG. 4 illustrates particulate test combustor (PTC) results for NanoG-CMtesting, in accordance with various embodiments.

FIG. 5 illustrates PTC results for NanoG-CM testing, in accordance withvarious embodiments.

FIG. 6 illustrates model results for in-flight mercury capture with acomposite sorbent in a high-sulfur flue gas, in accordance with variousembodiments.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to certain claims of the disclosedsubject matter, examples of which are illustrated in the accompanyingdrawings. While the disclosed subject matter will be described inconjunction with the enumerated claims, it will be understood that theyare not intended to limit the disclosed subject matter to those claims.On the contrary, the disclosed subject matter is intended to cover allalternatives, modifications, and equivalents, which can be includedwithin the scope of the presently disclosed subject matter as defined bythe claims.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Values expressed in a range format should be interpreted in a flexiblemanner to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range is explicitly recited. For example, aconcentration range of “about 0.1% to about 5%” should be interpreted toinclude not only the explicitly recited concentration of about 0.1 wt %to about 5 wt %, but also the individual concentrations (e.g., 1%, 2%,3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3%to 4.4%) within the indicated range.

In this document, the terms “a,” “an,” or “the” are used to include oneor more than one unless the context clearly dictates otherwise. The term“or” is used to refer to a nonexclusive “or” unless otherwise indicated.In addition, it is to be understood that the phraseology or terminologyemployed herein, and not otherwise defined, is for the purpose ofdescription only and not of limitation. Any use of section headings isintended to aid reading of the document and is not to be interpreted aslimiting; information that is relevant to a section heading may occurwithin or outside of that particular section. Furthermore, allpublications, patents, and patent documents referred to in this documentare incorporated by reference herein in their entirety, as thoughindividually incorporated by reference. In the event of inconsistentusages between this document and those documents so incorporated byreference, the usage in the incorporated reference should be consideredsupplementary to that of this document; for irreconcilableinconsistencies, the usage in this document controls.

In the methods of manufacturing described herein, the steps can becarried out in any order without departing from the principles of theinvention, except when a temporal or operational sequence is explicitlyrecited.

Furthermore, specified steps can be carried out concurrently unlessexplicit claim language recites that they be carried out separately. Forexample, a claimed step of doing X and a claimed step of doing Y can beconducted simultaneously within a single operation, and the resultingprocess will fall within the literal scope of the claimed process.

DEFINITIONS

The term “about” can allow for a degree of variability in a value orrange, for example, within 10%, within 5%, or within 1% of a statedvalue or of a stated limit of a range. When a range or a list ofsequential values is given, unless otherwise specified, any value withinthe range or any value between the given sequential values is alsodisclosed.

The term “hydrocarbon” as used herein refers to a functional group ormolecule that includes carbon and hydrogen atoms. The term can alsorefer to a functional group or molecule that normally includes bothcarbon and hydrogen atoms but wherein all the hydrogen atoms aresubstituted with other functional groups.

The term “pore” as used herein refers to a depression, slit, or hole ofany size or shape in a solid object. A pore can run all the way throughan object or partially through the object. A pore can intersect otherpores.

The term “solvent” as used herein refers to a liquid that can dissolve asolid, liquid, or gas. Nonlimiting examples of solvents are silicones,organic compounds, water, alcohols, ionic liquids, and supercriticalfluids.

The term “air” as used herein refers to a mixture of gases with acomposition approximately identical to the native composition of gasestaken from the atmosphere, generally at ground level. In some examples,air is taken from the ambient surroundings. Air has a composition thatincludes approximately 78% nitrogen, 21% oxygen, 1% argon, and 0.04%carbon dioxide, as well as small amounts of other gases.

The term “room temperature” as used herein refers to ambienttemperature, which can be, for example, between about 15° C. and about28° C.

As used herein, “substantially” refers to a majority of, or mostly, asin at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%,99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

As used herein, “nanocomposite” refers to a multiphase solid material inwhich one of the phases has at least one dimension of less than about1000 nm or in which less than an about 1000 nm repeat distance separatesat least some of the phases that make up the material. In someembodiments, one of the phases has at least one dimension in the rangeof about 1 nm-1000 nm or in which an about 1-1000 nm repeat distanceseparates at least some of the phases that make up the material; inother embodiments, the lower limit of the range can be less than about 1nm.

As used herein, “phase” refers to a region of space throughout which allphysical properties of a material are essentially uniform, such asphysical state, structure, and chemistry. For example, a liquid and agaseous state can be two different phases. For example, a carbonmaterial distributed on a substrate can be two different phases. Forexample, a carbon material distributed on a porous substrate can be twodifferent phases.

As used herein, “mineral” refers to a naturally occurring solid chemicalsubstance formed through biogeochemical processes, having, for example,characteristic chemical composition, highly ordered atomic structure,and specific physical properties.

DESCRIPTION

Various embodiments of the present invention provide methods andmaterials for the separation of a material from a gas. In someembodiments, the material can be a pollutant or an undesiredconstituent. In other embodiments, the material can be any suitablematerial. The gas includes the material; for example, the material canbe dissolved or suspended in the gas. The material includes a carbonnanocomposite sorbent. The method includes providing or obtaining thecarbon nanocomposite sorbent. The method includes contacting at leastsome of the material in the gas with the sorbent to form amaterial-sorbent composition. The method also includes separatingparticulates from the gas. The particulates include at least some of thematerial-sorbent composition. The separating gives a separated gashaving a lower amount of the material therein than the starting materialgas. Herein many specific examples of embodiments are given wherein thematerial separated is mercury, wherein the carbon nanocomposite sorbentis treated (e.g., promoted) with halides or halogens, or wherein thecarbon nanocomposite sorbent is treated with other materials. However,one of ordinary skill in the art will extrapolate from the examples andappreciate that embodiments encompass separation of any suitablematerial (such as, for example, any suitable pollutant, e.g., arsenic,selenium, and the like) from a gas using any suitable carbonnanocomposite material.

In various embodiments, the material separated from the gas is apollutant (e.g., an unwanted or undesirable constituent), and thematerial is desired to be removed from the gas to purify the gas. Thepollutant can include mercury. The pollutant can include elementalmercury. The pollutant can include oxidized mercury. In variousembodiments, the method can include providing a promoter. The promotercan be allowed to chemically react with at least a portion of thesorbent material, forming a promoted sorbent. The sorbent that contactsthe pollutant can include the promoted sorbent. In various embodiments,the promoter can be a halogen or halide promoter.

Reducing the Mercury Content of a Mercury-Containing Gas

In various embodiments, the present invention provides methods andmaterials for reducing the mercury content of a mercury-containing gas.The method includes providing or obtaining a carbon nanocompositesorbent. The method can include providing or obtaining a halogen orhalide promoter. The method can include promoting at least a portion ofthe sorbent material by chemically reacting the portion of the sorbentmaterial with the halogen or halide promoter to form a promoted sorbent.The method includes contacting at least part of the promoted sorbentwith the mercury to form a mercury-sorbent composition. In variousembodiments, the sorbent contacted with the mercury can also includeunpromoted sorbent. The method also includes separating at least some ofthe mercury-sorbent composition from the mercury-containing gas. Theseparation gives a cleaned gas having a lower mercury content than thestarting material gas. The mercury in the mercury-containing gas can beany suitable form of mercury, such as, for example, elemental mercury.The mercury can be suspended or dissolved in the gas. In someembodiments, the promoter can be HBr or NH₄Br, and in some examples, theHBr can be provided via degradation or reaction of ammonium bromide,NH₄Br. In some embodiments, the promoter (e.g., HBr) or promoterprecursor (e.g., NH₄Br) can be injected at an injection rate in the fluegas separately from the carbon nanocomposite sorbent or with the carbonnanocomposite sorbent (e.g., can be applied to the sorbentpre-injection).

Carbon Nanocomposite Sorbent

The methods provided by embodiments of the present invention use acarbon nanocomposite sorbent to remove a material from a gas, forexample, to remove mercury from a mercury-containing gas. Nanocompositesare composed of two of more phases such that the phases are intimatelyconnected to each other at nanoscale dimensions (e.g., 1000 nm or less).When these nanocomposites are highly porous, especially microporous ornanoporous, the intimate connectivity of the two nanocomposites canresult in high surface-areas as well as correspondingly high catalyticactivities. This can especially be the case when a catalytically activematerial, such as certain forms of carbon, is dispersed on a bulksubstrate having a high surface-area. Carbon nanocomposites can includea thin layer of graphene sheet coated on or intercalated into aninorganic support.

In some embodiments, the carbon nanocomposite sorbent can be about 50%or less carbon, or about 3 wt % to about 50 wt % carbon, or about 5 wt %to about 10 wt % carbon. In some embodiments, the carbon nanocompositesorbent can be about 1 wt % to about 99.5 wt % bulk substrate, or about50 wt % to about 97 wt % bulk substrate, or about 90 wt % to about 95 wt% bulk substrate (e.g., diatomaceous earth, smectite clays, and thelike).

The nanocomposite of the present invention can be any suitable carbonnanocomposite. In some examples, the nanocomposite can be a suitableform of carbon distributed on a suitably porous or suitably highsurface-area substrate. The nanocomposite can be produced or can becommercially obtained. In some embodiments, the nanocomposite iscommercially obtained, and further processing steps may be required tosuitably activate the carbon for separation of the material, such asseparation of the mercury. Further processing steps to suitably activatethe nanocomposite can include treatment with heat (e.g., calcining),treatment with base, treatment with a halide or halogen (e.g.,promoting), or combinations thereof. For example, in some embodiments,treatment of the nanocomposite with a halide or halogen can promote thenanocomposite to form active sites in the nanocomposite which cantransform mercury from elemental mercury into oxidized mercury (e.g.,mercury oxide). In some embodiments, no promotion of the nanocompositeis used. For example, in some embodiments, treatment of thenanocomposite with an acid or base can prepare the nanocomposite forpromotion using a halide or halogen or can prepare the nanocompositesuch that suitable reactivity is obtained. In other embodiments, notreatment with acid or base is used prior to promotion using a halide orhalogen or prior to using the sorbent to remove mercury or othermaterials from the gas.

The method can include contacting at least part of the nanocompositesorbent with the material in the gas, such as mercury, to form acomposition, such as a mercury-sorbent composition. The presentinvention is not dependent on any particular mechanism of action; solong as the material is removed from the gas using the carbonnanocomposite sorbent, the method is encompassed as an embodiment of thepresent invention. In some embodiments, the mercury is absorbed in itselemental form by the sorbent; the mercury-sorbent composition caninclude the sorbent and the elemental form of mercury. In someembodiments, the mercury is converted by the sorbent via a chemicalreaction, such as oxidation, such that the mercury from the gas istransformed into an oxide of mercury (e.g., HgO); the mercury-sorbentcomposition can include the sorbent and a transformed form of themercury such as a mercury oxide. In some embodiments, themercury-sorbent composition can include a combination of elementalmercury and transformed mercury, such as mercury oxide. In someexamples, the absorbing of elemental mercury or the transformation ofmercury can modify the sorbent, such that the sorbent is at leastslightly different after the composition is formed; e.g., aftertransformation of a particular atom of mercury to mercury oxide, theactive location of the sorbent that caused the transformation can beunreactive or less reactive.

In some examples, elemental mercury or transformed mercury can remainabsorbed to the sorbent until the mercury-sorbent composition has beenremoved in a later separation step. For example, elemental mercury ortransformed mercury can be absorbed, or reacted and absorbed, into oronto the sorbent composition, such that at least about 1 wt %, 3 wt %, 5wt %, 10 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt %, 60 wt %, 70 wt %, 80wt %, 90 wt %, 95 wt %, 96 wt %, 97 wt %, 98 wt %, 99 wt %, 99.9 wt %,99.99 wt %, or about 99.999 wt % or more of the mercury in themercury-containing gas stream is absorbed, or reacted and absorbed, intoor onto the sorbent composition. In some embodiments, elemental mercuryor transformed mercury can be released from the mercury-sorbentcomposition; for example, less than about 1 wt %, 3 wt %, 5 wt %, 10 wt%, 20 wt %, 30 wt %, 40 wt %, 50 wt %, 60 wt %, 70 wt %, 80 wt %, 90 wt%, 95 wt %, or less than about 99 wt % of the mercury can be releasedfrom the mercury-sorbent composition prior to separation of themercury-sorbent composition from the gas. In some examples, the majorityof absorbed elemental or transformed mercury can remain part of themercury-sorbent composition until the mercury-sorbent composition isremoved in a later separation step. In some examples, transformedmercury that is released from the mercury-sorbent composition can belater removed from the gas via the separation step. In some examples,elemental or transformed mercury that has been released from themercury-sorbent composition can contact carbon nanocomposite sorbent toform a mercury-sorbent composition, to be removed later via theseparation step.

In various embodiments, the carbon nanocomposite sorbent includesbinding sites that bind with mercury in the mercury-containing gas. Insome examples, the sorbent material includes carbon that is reacted orimpregnated with halogens or halides to form mercury binding sites inthe promoted sorbent. In some examples, the sorbent material can includecarbon that is activated at least in part by treatment with a base,wherein the base-activated carbon can react or become impregnated withhalogens, hydrogen halides, and Group V or VI halides to formmercury-binding sites in the promoted sorbent. In some examples, thebiding sites in the carbon react with mercury in the mercury-containinggas to form the mercury-sorbent composition. In some examples, at leasta portion of the binding sites of the carbon react with oxidized mercuryin the mercury-containing gas to form a mercury-sorbent composition.

In some embodiments, at least some of the carbon in the carbonnanocomposite is in the graphene form of carbon. The graphene form ofcarbon can, in some embodiments, include higher concentrations oflocations suitable as the active sites of the nanocomposite. In someexamples, certain parts of graphene carbon can have the highestconcentrations of locations suitable as the active sites of thenanocomposite: in some examples at the edges, in some examples innon-edge locations. Such locations suitable as active sites may beactivated via treatment with halide or halogen, as described herein. Invarious embodiments, the carbon in the carbon nanocomposite can be atleast about 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 10 wt %, 20 wt %, 30wt %, 40 wt %, 50 wt %, 60 wt %, 70 wt %, 80 wt %, 90 wt %, 95 wt %, 96wt %, 97 wt %, 98 wt %, 99 wt %, 99.9 wt %, 99.99 wt %, or more thanabout 99.999 wt % graphene form of carbon.

In some embodiments, the carbon nanocomposite sorbent has a meanparticle diameter greater than 40 micrometers, or greater than 60micrometers, or a particle size distribution greater than that of flyash or entrained ash in a flue gas stream to be treated, such that thecarbon nanocomposite sorbent and ash can be separated by physical meansin the separation step.

In one example, the nanocomposite can be a carbon nanocomposite that ispromoted for gas-phase Hg oxidation when a halide salt contained in theporous structure is decomposed during injection into a heated duct. Insome examples, the halide salt can be ammonium bromide. In someexamples, the carbon nanocomposite can include graphene. In someexamples, the non-carbon part of the nanocomposite includes a highsurface-area, porous, inorganic matrix.

Method of Forming a Carbon Nanocomposite Sorbent

The carbon nanocomposite sorbent can be obtained, it can be synthesized,or any combination thereof. For example, an obtained carbonnanocomposite material may need further treatment before it is suitablefor use in an embodiment of the method of the present invention. Variousembodiments provide a method of forming the carbon nanocompositesorbent, a carbon nanocomposite sorbent formed thereby, or a combinationof the carbon nanocomposite sorbent with a mercury-containing gas. Forexample, the method of making the carbon nanocomposite sorbent caninclude providing or obtaining a carbon precursor, wherein the carbonprecursor provides the carbon in the carbon nanocomposite sorbent. Themethod can include providing or obtaining a substrate material, whereinthe substrate material provides the bulk substrate in the carbonnanocomposite sorbent. The method can include contacting the carbonprecursor and the substrate material to provide a nanocomposite startingmaterial. The method can include heating the nanocomposite startingmaterial. Heating the nanocomposite starting material provides thenanocomposite sorbent. Before use, the nanocomposite sorbent canoptionally be subjected to processing steps, such as treatment withbase, or such as treatment with a halogen or halide, which can allowformation of active sites on the carbon nanocomposite that can reactwith elemental mercury to transform the mercury, for example, intooxidized mercury (e.g., mercury oxide).

In some examples, using a substrate such as a clay (e.g., the substrateallowing for an open and porous substructure), a carbohydrate (e.g.,carbon precursor) can be contacted with the substrate. The resultingmixture can be heated, which creates a carbon layer with a low carbondensity that covers the open porous structure of the substrate material.In some embodiments, as the mixture is heated, the substrate can swell.The carbon layer can be created by chemical reactions of the carbonprecursor caused by the heating step, including decomposition reactions,including for example pyrolysis, dehydration, or decarboxylationreactions. In some embodiments, the carbon layer created includes thegraphene form of carbon, for example as graphene ribbons. The grapheneform of carbon, especially at its edges, can, in some embodiments,include higher concentrations of locations suitable as the active sitesof the nanocomposite. The carbon coats the surfaces of the clayparticles, which can be randomly stacked in a highly porous matrix. Inexamples, a halide or halogen can be introduced to the sorbent,promoting the carbon and enhancing the reactivity of the sorbent tomercury. The halide or halogen can be introduced in various forms.

In some embodiments, a promoted sorbent can be produced “in-flight.”This can be accomplished by, for example, contacting the vapors of anycombination of halogens, in-flight, with the carbon nanocompositesorbent. In-flight promotion of the carbon nanocomposite sorbent can beaccomplished by contacting the vapors of any combination of halogenswith the carbon nanocomposite sorbent in a stream of transport air or apolluted gas stream containing mercury from which mercury is to beremoved. The particles can be dispersed in a stream of transport air (orother gas), which also conveys the halogen-/halide-promoted carbonsorbent particles to the flue gas duct, or other polluted gas stream,from which mercury is to then be removed. In some embodiments, theparticles can be dispersed directly in a flue gas stream.

The simplicity and resulting cost savings of in-flight promotion can beadvantageous. Capital equipment costs, operation costs, andtransportation costs of a treatment facility can be eliminated.In-flight preparation can use existing hardware and operation proceduresand can help to ensure the promoted sorbent is always fresh and, thus,more reactive. In-flight preparation allows for rapid on-site tailoringof the degree of promoting the sorbent in order to ensure adequatereactivity to match the requirements of flue gas changes, such as may beneeded when changing fuels or reducing loads, thus further optimizingthe economics and effectiveness of mercury capture.

Carbon Precursor

The method of making the carbon nanocomposite sorbent can includeproviding or obtaining a carbon precursor, wherein the carbon precursorprovides the carbon in the carbon nanocomposite sorbent. The carbonlayer in the nanocomposite can be created by chemical reactions of thecarbon precursor caused by the heating step, including decompositionreactions, including for example pyrolysis, dehydration, ordecarboxylation reactions.

The carbon precursor can include any suitable carbon precursor, suchthat the heating step transforms the carbon precursor and the substrateinto a suitable carbon nanocomposite sorbent. For example, the carbonprecursor can be any sugar source such as a carbohydrate (saccharide),including, for example, brown sugar, barley sugar, caramel, cane sugar,corn syrup, molasses, sugar or sugar processing wastes such as beetsugar waste, cane sugar waste, and the like. The carbon precursor can beany suitable starch or source of starch.

In some examples, the carbon precursor can be present in from about 1 wt% to about 99 wt %, about 20 wt % to about 80 wt %, or about 40 wt % toabout 60 wt % of the starting material for the carbon nanocompositesorbent. In some examples, the carbon precursor can be present in fromabout 50% or less carbon, or about 3 wt % to about 50 wt % carbon, orabout 5 wt % to about 10 wt % carbon of the starting material for thecarbon nanocomposite sorbent. Wt % in this paragraph refers to thepercentage by weight based on the total weight of the carbon precursorand the substrate material.

Substrate Material

The method of making the carbon nanocomposite sorbent can includeproviding or obtaining a substrate material, wherein the substratematerial provides the bulk substrate in the carbon nanocompositesorbent.

The substrate material can include any suitable substrate material, suchthat the heating step transforms the carbon precursor and the substratematerial into a suitable carbon nanocomposite sorbent. The substrate caninclude any suitable porous material. For example, the substratematerial can be diatomaceous earth, zeolites, porous minerals (e.g.,clays) including, for example, smectites (e.g., montmorillonite,bentonite, nontronite, saponite), kaolins, illites, chlorites,sepiolite, or attapulgites. In some examples, the substrate can includepolymers, non-metals, metals, metalloids, ceramics or mixtures, andblends, as well as composites and alloys thereof. The materials can besynthetic or naturally occurring or naturally derived materials.Examples of synthetic polymers include any common thermoplastics andthermosetting materials. Examples of metals include aluminum, titanium,copper, steel, and stainless steel. Examples of ceramics include anyform of alumina, zirconia, titania, and silica. Examples of naturallyoccurring or naturally derived materials include wood, wood composites,paper, cellulose acetate, and geologic formations such as granite orlimestone. Examples of non-metals include various forms of carbon suchas graphite or carbon. Examples of metalloids include silicon orgermanium. The porous material can be a construction material such asconcrete or asphalt.

In some examples, the substrate material can be present in from about 1wt % to about 99 wt %, about 20 wt % to about 80 wt %, or about 40 wt %to about 60 wt % of the starting material for the carbon nanocompositesorbent. Wt % in this paragraph refers to the percentage by weight basedon the total weight of the carbon precursor and the substrate material.

Contacting and Heating

The method of making the carbon nanocomposite sorbent can includecontacting the carbon precursor and the substrate material to provide ananocomposite starting material. The method can include heating (e.g.,providing energy to) the nanocomposite starting material. Heating (orother means of providing energy to) the nanocomposite starting materialprovides the nanocomposite sorbent.

The contacting can take place in any suitable fashion. The contactingmixes the carbon precursor and the substrate material, such that whenthe conglomeration is heated (or subjected to any other suitable sourceof energy), the carbon nanocomposite sorbent is formed. The contactingcan be performed such that the carbohydrate is approximately evenlydistributed on the substrate. In some examples, water or another solventcan be added to help distribute the carbon precursor on the substrate.In examples where water is included in the mixture of the carbonprecursor and the substrate, the conglomeration can be dried prior tothe heating. The drying can occur in any conventional manner (e.g.,convective, conductive, microwave, and the like), including by heatingnear or above the boiling point of the solvent, in the case of water(e.g., 50° C.-120° C. or higher), at atmospheric pressure, underpressure, or under a vacuum.

The contacted composition of the carbon precursor and the substrate canthen be heated to form the carbon nanocomposite sorbent. The heating issufficient to cause the chemical reactions that transform the carbonprecursor into the form of carbon present in the carbon nanocomposite(e.g., decomposition reactions) including, for example, pyrolysis,dehydration, or decarboxylation reactions. The heating can take place atany suitable temperature, such that the carbon nanocomposite issufficiently formed, for example about 50° C., 100° C., 200° C., 300°C., 400° C., 500° C., 600° C., 700° C., 800° C., 900° C., 1000° C.,1100° C., or about 1200° C. The heating can take place for any suitabletime, such that the carbon nanocomposite is sufficiently formed, forexample, greater than about 1 min, 2 min, 5 min, 10 min, 30 min, 1 h,1.5 h, 2 h, 3 h, 4 h, 5 h, 10 h, or greater than about 24 h. The heatingcan take place in any suitable apparatus, for example, a unit thatallows heated air to flow around the mixture being heated or a furnace.The heating can be accelerated, or lengthened, depending on theapparatus and the nanocomposite material.

Halogen or Halide Promoter

A “halogen” is defined as a member of the elements included in GroupVIIA of the periodic table (Group VIIA [CAS] corresponds to Group VIIB[IUPAC]). The molecular elemental form of the halogens, including F₂,Cl₂, Br₂, and I₂, can be relatively uncreative with elemental mercury ina hot flue gas. Any halogen ion, gas, or compound can be a promoter.

Embodiments of the method for reducing the mercury content of amercury-containing gas include providing or obtaining a halogen orhalide promoter. The method includes promoting at least a portion of thesorbent material. The promoting of the sorbent material includeschemically reacting or impregnating the portion of the sorbent materialwith the halogen or halide promoter. The halogen or halide promoter canbe derived from reaction or degradation of another compound (e.g., apromoter precursor). The promoting of the sorbent material gives apromoted sorbent. The promoting of the sorbent material can occur beforeinjection into a gas stream, during injection into a gas stream, afterinjection into a gas stream, or a combination thereof, wherein the gasstream can be a mercury-containing gas stream, a transport stream, or acombination thereof. In some examples, the promoter can be added to thesorbent before the promoter and the sorbent react, such that the heat ofthe gas stream into which the promoter is added causes the promoting ofthe sorbent. For example, the promoter can be added as a gas, as a gasdissolved in a liquid, or as a solid such as a salt, or other substance(e.g., acid) dissolved in liquid (e.g., water). In examples wherein thepromoter is added in a liquid such as water, the water can be allowed todry, which can allow the promoter to adhere to, impregnate, or reactwith the nanocomposite sorbent, or a combination thereof. In someexamples, a pre-added promoter can be an ammonium salt, such as anammonium chloride, an ammonium bromide, or an ammonium iodide,including, for example, mono-, di-, tri-, or tetraalkyl ammoniumhalides, or NH₄ ⁺ halide salts. In some examples, the promoter can beadded to the sorbent near to or at the time of promoting; for example,the promoter can be added to a gas stream with the sorbent or such thatit contacts the sorbent within a heated gas stream, such as amercury-containing gas stream or a feed gas stream. In some examples,the promoter can be NH₄Br.

In some embodiments, the promoter can be HBr, and in some examples, theHBr can be provided via degradation or reaction of a promoter precursorsuch as ammonium bromide, sodium bromide, or calcium bromide. Thepromoter can be HCl, and in some examples, the HCl can be provided viadegradation or reaction of a promoter precursor such as ammoniumchloride, sodium chloride, or calcium chloride. The promoter can be HF,and in some examples, the HF can be provided via degradation or reactionof a promoter precursor such as ammonium fluoride, sodium fluoride, orcalcium fluoride. In some examples, the promoter (e.g., HBr or HCl) orpromoter precursor (e.g., NH₄Br, NaBr, CaBr₂, NH₄Cl, NaCl, CaCl₂) can beinjected in the flue gas separately from the carbon nanocompositesorbent or with the carbon nanocomposite sorbent (e.g., can be appliedto the sorbent pre-injection, injected simultaneously at the samelocation, or injected simultaneously at different locations).

Not intending to limit embodiments to any particular mechanism ofaction, in various embodiments, adding a halogen, or a proton from ahydrogen halide acid, to a basic carbene site on the carbon edgestructure forms a carbocation that accepts electrons from the neutralmercury atom forming the oxidized mercury species that is bound to thesorbent surface. The reactive site can also generate reactive halogenradicals or carbon radicals at the active sites on the carbon. Thus thecarbon nanocomposite sorbent provides a highly reactivehalogen-containing reagent that can oxidize the mercury and promote itscapture on the carbon nanocomposite sorbent. In some embodiments, asorbent that contains bromine or that is promoted by bromine or abromine reagent is expected to be more reactive than the correspondingsorbent promoted by chlorine or a chlorine reagent and less expensivethan the sorbent promoted by iodine or an iodine reagent.

Reactions of halogens and acidic species with the binding sites on thepromoted carbon nanocomposite sorbent can create active sites foroxidizing mercury. Other metal ions, such as boron, tin, arsenic,gallium, Sb, Pb, Bi, Cd, Ag, Cu, Zn, Se, or other pollutants, can alsoreact with the oxidation sites on the carbon.

In some embodiments, the halogen or halide promoter that is added to,and reacts with, the carbon nanocomposite sorbent can include, by way ofillustration and not limitation, a molecular halogen in vapor or gaseousform, a molecular halogen in an organic solvent, a Group V or Group VIhalide, such as PBr₃ or SCl₂, respectively, in vapor, liquid, orsolution form (e.g., in water or a non-aqueous solvent such as analcohol or other organic solvent).

Embodiments are also provided in which the organic solvent can include achlorinated hydrocarbon, such as dichloromethane, a hydrocarbon solvent,including for example, petroleum ether, ligroin, pentane, hexane,toluene, and benzene, carbon disulfide, a waste solvent, an ether, arecycled solvent, a supercritical solvent, such as supercritical CO₂,water (though not in the case of a Group V or Group VI halide), andothers as will be apparent to those of skill in the art.

In some embodiments, the method can include adding an additional halogenor halide promoter to the promoted sorbent. The additional halogen orhalide can be any halogen or halide described herein as suitable as thefirst halogen or halide. For example, the additional halogen or halidepromoter can include HI, HBr, HCl, a Group V element with halogen, or aGroup VI element with halogen.

In various embodiments, the step of promoting at least a portion of thesorbent material can occur at least partially before the contacting ofthe mercury-containing gas with the sorbent. In some examples, the stepof promoting at least a portion of the sorbent can occur at leastpartially during the contacting of the mercury-containing gas with thesorbent. In some examples, the carbon nanocomposite sorbent can beinjected into a gas stream at an injection rate, in which at least onepromoter is injected separately at an injection rate into a gas streamwhereby in-flight reaction produces the promoted sorbent. In someexamples, the promoter can be reacted in the gas phase or as a vapor. Insome examples, the promoter is added at from about 0.01 g to about 200g, or about 0.1 g to about 100 g, or about 1 g to about 30 g per 100grams of carbon nanocomposite sorbent material. In some examples, eitherone or both of the gas streams into which the sorbent and the promoterare injected can be a transport gas, a flue gas stream (e.g., amercury-containing gas), or a combination thereof. In some examples, thepromoter injection rate and the sorbent injection rate into the gas aredetermined, at least in part, from the monitored mercury content of thecleaned gas.

Contacting the Sorbent and the Mercury in the Mercury-Containing Gas

In embodiments of the method for reducing the mercury content of amercury-containing gas, the method can include contacting at least partof the promoted sorbent with the mercury in the mercury-containing gas.Contacting the promoted sorbent with the mercury in themercury-containing gas includes contacting the promoted sorbent with themercury-containing gas. Contacting the promoted sorbent with the mercuryforms a mercury-sorbent composition. The contacting can occur in anysuitable location. For example, the contacting can occur in the gas. Inanother embodiment, the contacting can occur in an aqueous liquid. Inanother example, the contacting can occur in the gas, and subsequentlycontacting can also occur in an aqueous phase such as a scrubber.

In various embodiments, measurement of mercury emissions can be used asfeedback to assist in controlling the sorbent injection rate. Tightercontrol on the sorbent and optional component(s) levels can be achievedin this way, which can help to ensure mercury removal requirements aremet with the minimum promoter and sorbent requirements, thus minimizingthe associated costs. In an embodiment, the mercury emissions arecontinuously measured downstream of the injection location, for example,in the exhaust gas at the stack. In various embodiments, contacting atleast part of the promoted sorbent with the mercury in themercury-containing gas can occur between particulate control devices.

Separating at Least Some of the Mercury-Sorbent Composition from theMercury-Containing Gas

In embodiments of the method for reducing the mercury content of amercury-containing gas, the method includes separating at least some ofthe mercury-sorbent composition from the gas. The separation gives acleaned gas, having a lower mercury content than starting materialmercury-containing gas. In some embodiments, separating at least some ofthe mercury-sorbent composition from the mercury-containing gascomprises separating particulates from the gas, wherein the particulatescomprise at least some of the mercury-sorbent composition.

In some examples, the step of separating particulates from themercury-containing gas includes separating the particulates from the gasin a particulate separator. The particulate separator can be anysuitable separator. The particulate separator can include one or morecyclones, electrostatic precipitators, fabric separators, scrubbers, orother particulate removal devices as are known in the art. In someembodiments, an electrostatic precipitator can be used, followed by ascrubber. In other embodiments, an electrostatic precipitator can beused without a scrubber, or another particulate separator can be used.Some devices that can function as particulate separators can also haveother functions, for example a scrubber can also remove SO₂ or SO₃ fromthe gas stream, as described further below. In embodiments that includecontacting of the mercury with a sorbent in an aqueous phase, e.g. in ascrubber, the removal of mercury from the gas that occurs within theaqueous phase by reaction or interaction of the mercury with the sorbentin the aqueous phase can be considered separation of the mercury-sorbentcomposition from the gas.

In some examples, by separating the particulates from themercury-containing gas, at least about 20 wt %, 30 wt %, 40 wt %, 50 wt%, 60 wt %, 70 wt %, 80 wt %, 90 wt %, 95 wt %, 96 wt %, 97 wt %, 98 wt%, 99 wt %, 99.9 wt %, 99.99 wt %, or about 99.999 wt % or more mercurycan be removed from the mercury-containing gas stream. As discussedherein, the mercury can be removed in the form of elemental mercury, inthe form of a transformed mercury, such as a oxidized mercury (e.g.,mercury oxide).

Scrubber

In various embodiments of the method for reducing the pollutant contentof a pollutant-containing gas, an aqueous scrubber can be used. Anaqueous scrubber allows an aqueous liquid or aqueous slurry to contactthe gas stream. A scrubber can spray, nebulize, or otherwise distributeaqueous material in the space through which the gas stream flows thereinsuch that the surface area of the liquid that contacts the gas in thescrubber is increased. The aqueous solution can fall to the bottom ofthe scrubber, where it can be recycled back to the top, or removed to beregenerated, cleaned, or replaced. The aqueous scrubber can be anysuitable aqueous scrubber. In some examples, the aqueous scrubber canremove one or more pollutants from the gas stream.

A scrubber can remove particulate from a gas stream. For example, when agas stream including particulates passes through the scrubber,particulates that contact droplets or other forms of aqueous solutioncan become stuck or immersed in the aqueous solution. As the aqueoussolution falls to the bottom of the scrubber, the particles can fallwith it. The aqueous solution can be recycled back to the top of thescrubber with at least some of the particles in it. The aqueous solutioncan be any suitable consistency, such as a free-flowing clear liquid, aliquid having suspended solid, or slurry of any suitable viscosity.Continuously or batchwise the aqueous solution in the scrubber can becleaned or replaced, removing, for example, particles, pollutant, orpollutant-byproduct. In one example, sorbent in the aqueous solution canbe separated and regenerated, such as described in US 2007/0167309.

In various embodiments, the method can include removing at least someSO₂ or SO₃ from the pollutant-containing gas (e.g. reducing theconcentration of SO₂ or SO₃). The removal can be done in any suitableway. In some examples, an aqueous scrubber can remove SO₂ or SO₃ fromthe gas stream, for example, by reaction with SO₂ or SO₃ with chemicalcompounds present in the water in the scrubber. Some examples ofchemical compounds that can be included in the water in the scrubberthat can react with SO₂ or SO₃ include salts that form basic solutionsin water, such as, for example, carbonate (CO₃ ⁻²), bicarbonate (HCO₃⁻), or carbamate (OCONH₂ ⁻) salts, having any suitable counterion, suchas, for example, ammonium (NH₄ ⁺), sodium (Na⁺), potassium (K⁺),magnesium (Mg⁺²), or calcium (Ca⁺²). For example, the basic salt can beammonium carbonate ((NH₄)₂CO₃), ammonium bicarbonate ((NH₄)HCO₃), orammonium carbamate ((NH₄)OCONH₂).

In various embodiments, a promoter or promoter precursor can be in theaqueous solution of the scrubber. In some embodiments, a promoter (e.g.,HBr) can be added directly to the water in the aqueous scrubber. In someexamples, a promoter precursor (e.g., NH₄Br) can be added directly tothe water in the aqueous scrubber, where it can decompose to form thepromoter (e.g., HBr). The promoter precursor can be injected into hotgas (e.g., a hot carrier gas, or the flue gas stream) where it can beconverted into the promoter, and subsequently the gas stream can enterthe scrubber, where the precursor can be absorbed or dissolved in thewater in the scrubber. The promoter or promoter precursor can enter anysuitable part of the scrubber in any suitable way, for example, it canenter the flue gas stream prior to entering the scrubber, it can beseparately injected into the gas phase of the scrubber, or it can beinjected into the aqueous phase of the scrubber.

In some embodiments, the aqueous solution in the scrubber can includeactivated carbon nanocomposite sorbent. In such embodiments, thescrubber can remove one or more pollutants from the gas stream, such asmercury, by allowing the activated sorbent in the aqueous phase to reactwith or absorb one or more pollutants from the gas stream. Thenanocomposite can enter the scrubber in any suitable location in anysuitable way, for example, it can enter the flue gas stream prior toentering the scrubber, it can be separately injected into the gas phaseof the scrubber, or it can be injected into the aqueous phase of thescrubber. Optionally, aqueous solutions that include activated carbonnanocomposite sorbent can include other chemicals that can react withpollutants in the gas stream, such that the scrubber can remove morethan one type of pollutant. For example, in addition to activated carbonnanocomposite sorbent, an aqueous scrubber solution can also includebasic salts that can react with SO₂.

In some examples, the carbon nanocomposite can be activated in thescrubber, such as in embodiments that include the promoter in the waterof the scrubber. The carbon nanocomposite can be added directly to thescrubber (e.g. to the gas phase or liquid phase), or before the scrubberin the gas stream flowing into the scrubber. The carbon nanocompositecan be added at any suitable point between a particulate control device(e.g. ESP) and a scrubber. In some examples, both the carbonnanocomposite and the promoter or promoter precursor can be injectedinto a hot gas stream (e.g. hot carrier gas, or the flue gas stream)where promoted carbon nanocomposite sorbent can form prior to entry intothe scrubber. In some embodiments, a carbon nanocomposite can be coatedwith a promoter or promoter precursor, and the coated carbonnanocomposite can be injected into a hot gas (e.g., a hot carrier gas,or the flue gas stream) where it can convert into the promoter, andsubsequently be absorbed in the water in the scrubber.

In embodiments including an ESP and a scrubber, optionally carbonnanocomposite can be used for pollutant removal prior to an ESP and alsoin a wet scrubber. In such an embodiment, the ESP can removenanocomposite-pollutant. Alternatively, the carbon nanocomposite can beused in the scrubber and not prior to the ESP. Alternatively, the carbonnanocomposite can be used only prior to the ESP and not in the scrubberor not predominantly in the ESP.

Alkaline Component

In some examples, the method of removing mercury from amercury-containing gas stream can include injecting an alkaline (e.g.,basic) component into the mercury-containing gas. In some examples, thealkaline component includes an oxide, hydroxide, carbonate, or phosphateof an alkali or alkaline-earth element.

In various examples, the addition of an alkaline component separately orwith the carbon nanocomposite sorbent can result in improved mercurycapture, in some examples exceeding that of both the promoted andunpromoted carbon nanocomposite sorbent. Various factors can impact theeffectiveness of the alkaline addition, such as, for example, flue gaspollutants, flue gas constituents (e.g., SO₂, NO_(x), HCl, and thelike), operating temperature, mercury form, and mercury concentration.In some examples, the alkaline-to-activated-carbon ratio can be adjustedto optimize for a given set of site conditions.

Stabilizing Agent

In some examples, a stabilizing agent can be added to the promotedsorbent. The stabilizing agent can be a mercury stabilizing agent. Insome embodiments, a method is provided whereby a mercury stabilizingagent is added to a promoted carbon sorbent to produce a bifunctionalsorbent. Such stabilizing agent(s) can be sequentially added, eitherbefore or after the addition and reaction of the halogen/halide. In someembodiments, the halogen/halide includes Br or HBr, and themercury-stabilizing agent can include S, Se, H₂S, SO₂, H₂Se, SeO₂, CS₂,P₂S₅, and combinations thereof.

Regeneration of Sorbent

In any of the embodiments of the method or the material for separatingmercury from a mercury-containing gas stream, the carbon sorbent can beregenerated; sorbent-poisoning pollutants from the flue gas can beremoved; and the sorbent can be re-promoted to restore mercury sorptionactivity. The regenerated sorbent can then be used again in the method.Detailed examples of sorbent regeneration techniques are described inco-pending, commonly owned PCT patent application No. PCT/US04/12828,titled “PROCESS FOR REGENERATING A SPENT SORBENT,” which is herebyincorporated by reference in its entirety.

Example Process

In various embodiments, the carbon nanocomposite sorbent, method ofmercury removal, and optional additives discussed herein haveapplicability to mercury control from the product or effluent gas orgases from gasification systems, syngas generators, and othermercury-containing gas streams, in addition to the flue gas fromcombustion systems. Thus, it should be understood that the termscombustion system and flue gas as used throughout this description canapply equally to gasification systems and syngas or fuel gas, as will beunderstood by those skilled in the art.

Referring now to FIG. 1, there is shown a block flow diagramillustrating methods for preparation of promoted carbon sorbents, inaccordance with various embodiments. Block 10 illustrates providingcarbon nanocomposite sorbent and adding a halogen or halide promoterthat reacts with the carbon, illustrated at block 20, to produce apromoted carbon nanocomposite sorbent. In embodiments where a halogen orhalide is added in, for example, a solvent, solvent removal can be usedas illustrated by block 20A. Block 30 indicates adding an optionalsecondary component illustrated at block 30 that reacts with the resultof block 20 or 20A to produce a promoted carbon nanocomposite sorbent.In embodiments where the halogen or halide promoter and/or secondarycomponent are added in, for example, a solvent, solvent removal can beused as illustrated by block 30A.

In FIG. 1, the steps leading to step 50 produce promoted sorbent priorto treatment of the flue gas stream with the promoted sorbent. Theaddition of one or more promoters, and the reactions or interactionswith the promoters that lead to promotion of the sorbent, can occur inany suitable location. In some examples, the sorbent can be promoted ina hot-gas stream, such as in a flue gas stream, or such as in a hotcarrier gas stream. In some embodiments, the promoter can be added tothe sorbent before the sorbent is injected into a hot-gas stream. Insome embodiments, the promoter can be added to the hot-gas stream withthe sorbent, referred to herein as “in-flight” promotion of the sorbent.Thus, in some embodiments, prior to step 50, the promoter and thesorbent can be injected together or separately into the flue gas streamor another hot-gas stream.

Referring still to FIG. 1, path 10-40 includes providing a carbonnanocomposite sorbent as illustrated at block 10 and adding a halogen orhalide promoter and a secondary component to the sorbent together, withwhich they can react as illustrated by block 40, producing a promotedcarbon nanocomposite sorbent. In embodiments where one or morecomponents are added in solvent, a solvent removal step can be providedas illustrated by block 40A.

Referring still to FIG. 1, also illustrated are embodiments in which, asillustrated by block 50, a flue gas stream is treated with promotedcarbon nanocomposite sorbent prepared as described herein.

Referring now to FIG. 2, there is illustrated a theory developed fromscientific evidence to explain the nature of the promoting compounds,which is not intended to limit embodiments of the present invention toany specific theory of operation. The method of the present inventionencompasses any removal of mercury from a gas using a carbonnanocomposite in any suitable way.

For example, as illustrated in FIG. 2, hydrogen bromide can react withthe unsaturated structure of the carbon nanocomposite sorbent. Thehydrogen bromide can be provided by, for example, ammonium bromide. Thereactive part of the carbon on the carbon nanocomposite sorbent can be,by way of illustration only, a carbene species on the edge of thegraphene sheet structures of the carbon. Molecular bromine or otherbromine compounds can react to form a similar structure, with a positivecarbon that is active for oxidizing the mercury with subsequent captureby the sorbent.

The formation of the bromide compound with carbon increases thereactivity of the carbon nanocomposite toward mercury and otherpollutants. Additionally, the resulting bromide compound is uniquelysuited to facilitate oxidation of the mercury. The effectiveness of theoxidation may result from the promotion effect of the halide exerted onthe developing positive charge on the mercury during the oxidation,known in the chemical arts as a specific catalytic effect. Thus, as themercury electrons are drawn toward the positive carbon, the halide anionelectrons can push in from the other side, stabilizing the positivecharge developing on the mercury and lowering the energy requirement forthe oxidation process. Bromide is especially reactive, owing to thehighly polarizable electrons in the outer 4 p orbitals of the ion. Thus,adding HBr or Br₂ to the carbon nanocomposite can form a similar carbonbromide, in which the positive carbon can oxidize the mercury with theassistance of the bromide ion.

FIG. 3A shows a schematic flow diagram of mercury control system 100including preparation of promoted carbon sorbents and flue gas mercuryreduction, in accordance with embodiments of the present invention.There is provided carbon nanocomposite sorbent reservoir 110, anoptional halogen/halide promoter reservoir 120, an optional secondarycomponent reservoir 130, and an optional alkali component reservoir 180,each of which with corresponding flow control device(s) 201, 202, 203,and 207/208/209, respectively. Reservoirs 110, 120, and 130 withcorresponding flow controllers 201, 202, and 203 can be used inconjunction with transport lines 113 and 115 independently, together, ornot at all. For example, reservoir 110 with controller 201 can be usedwith transport line 113 independently and separately to inject materialat injection point 114, while at the same time, optional reservoirs 120and/or 130 with corresponding flow controllers 202 and/or 203 can beused with transport line 115 to independently and separately injectmaterial at injection point 116. In conjunction with the optional alkalicomponent reservoir 180, optional flow control devices 207, 208, and 209can be used independently, together, or not at all.

Reservoirs 110, 120, 130, and 180 connect through their respective flowcontrol devices and via associated piping, to transport lines 113 and115. Optional alkali component reservoir 180 can also connect, throughrespective flow control devices and via associated piping, to transportline 118. A source of air, nitrogen, or other transport gas(es) isprovided by gas source 169 to transport line 113 to entrain materialsdischarged from reservoirs 110, 120, 130, and 180 and to inject suchmaterials, via injection point 114, into polluted flue gas stream 15. Asource of air, nitrogen, or other transport gas(es) is provided by gassource 170 to transport line 115 for the purpose of entraining materialsdischarged from reservoirs 110, 120, 130, and 180 and injecting suchmaterials, via injection point 116, into polluted flue gas stream 15. Asource of air, nitrogen, or other transport gas(es) can be provided bygas source 171 to transport line 118 for the purpose of entrainingmaterials discharged from reservoirs 180 and injecting such materials,via injection point 119, into flue gas stream 15. Gas sources 169, 170,and 171 can be the same or different, as desired. Alternatively,transport gas(es) can be provided to transport lines 113, 115, and 118by gas source 170 (connection from source 170 to transport line 113and/or 118 not shown). Although gas sources 169, 170, and 171 are shownin FIG. 3A as compressors or blowers, any source of transport energyknown in the art can be acceptable, as will be appreciated by those ofordinary skill in the art. For example, 169 can be a pump in the casethat 120 is added as a liquid.

For clarity, single injection points 114, 116, and 119 are shown in FIG.3A, although one of ordinary skill in the art will understand thatmultiple injection points are within the scope of the present invention.Optical density measuring device(s) 204 is connected to transport line113 or 115 (or 118, not shown) to provide signals representative of theoptical density inside transport line 113, 115, or 118 as a function oftime.

Downstream from injection point 116 and 119 is provided particulateseparator 140. By way of illustration and not limitation, particulateseparator 140 can include one or more fabric filters, one or moreelectrostatic precipitators (hereinafter “ESP”), or other particulateremoval devices as are known in the art. It should be further noted thatmore than one particulate separator 140 can exist, sequentially or inparallel, and that injection point 116 and 119 can be at a locationupstream and/or downstream of 140 when parallel, sequential, orcombinations thereof exist. Particulate separator 140 can produce atleast a predominantly gaseous (“clean”) stream 42 and a stream 141including separated solid materials. A sorbent/ash separator 150 canseparate stream 141 into a largely ash stream 152 and a largely sorbentstream 151. Alternatively, not shown, stream 141 can be disposed of as awaste stream or sent directly to the optional sorbent regenerator 160.Stream 151 can then be passed to an optional sorbent regenerator 160,which yields a regenerated sorbent stream 161 and a waste stream 162.

An optional aqueous scrubber 190 is provided after optional ESP 140. Theaqueous scrubber 190 can be provided with ESP 140 or without ESP 140.Scrubber 190 can remove particulates from the gas stream, can removepollutants such as SO₂ from the gas stream via chemical reaction withbasic aqueous liquid, can remove pollutants such as mercury from the gasstream via reaction or absorption with activated carbon nanocompositesorbent in the scrubber, or any suitable combination thereof. Inaddition to, or as an alternative to, the injection and promotion ofcarbon nanocomposite sorbent prior to unit 140, promoter 120 or promoterprecursor can be provided to the aqueous scrubber 190. The promoter orpromoter precursor can be injected into gas stream 42, or can beprovided directly into the scrubber (transport lines between 120/130 and190 not shown). The promoter or promoter precursor can be providedbefore or into the scrubber 190 as a carbon nanocomposite sorbent coatedor combined with the promoter or promoter precursor. Promotion of acoated or combined sorbent/precursor can occur in the scrubber 190, inthe gas stream 42 prior to the scrubber, or in a heated carrier gas line(not shown) that brings the activated nanocomposite to 42 or 190. Inaddition to, or as an alternative to, the injection and promotion ofcarbon nanocomposite sorbent prior to unit 140, carbon nanocomposite canbe provided to the aqueous scrubber 190. The carbon nanocomposite can beinjected into gas stream 42, or can be provided directly into thescrubber (transport lines between 110 and 190 not shown). The aqueoussolution in the scrubber can be regenerated or replaced in a batchwiseor continuous process, to remove absorbed particulate, absorbedpollutant, or absorbed pollutant byproducts.

An optional continuous emission monitor (hereinafter “CEM”) 205 formercury is provided in exhaust gas stream 35 to provide electricalsignals representative of the mercury concentration in exhaust stream 35as a function of time. The optional mercury CEM 205 and flow controllers201, 202, 203, 207, 208, and 209 are electrically connected via optionallines 227 (or wirelessly) to an optional digital computer (orcontroller) 206, which receives and processes signals and can controlthe preparation and injection of promoted carbon sorbent into pollutedflue gas stream 15.

In an example operation, a carbon nanocomposite sorbent and/or anoptional promoter, and/or an optional alkali component, can be injectedinto polluted flue gas stream 15. After contacting the injected materialwith the polluted flue gas stream 15, the injected material reduces themercury concentration, transforming polluted flue gas into reducedmercury flue gas stream 25. The injected material can be removed fromthe reduced mercury flue gas stream 25, by separator 140, disposed of orfurther separated by optional separator 150, and disposed of orregenerated by an optional regenerator 160, respectively. Alternativelyor in addition, scrubber 190 can remove SO₂, pollutants such as mercuryvia promoted carbon nanocomposite, remove particulate, or anycombination thereof. The reduced mercury “clean” flue gas stream 42and/or 35 is then monitored for mercury content by an optional CEM 205,which provides corresponding signals to an optional computer/controller206. Logic and optimization signals from 206 then can adjust flowcontrollers 201, 202, 203, 207, 208, 209 to maintain the mercuryconcentration in exhaust stream 35 within desired limits, according tocontrol algorithms well known in the art. Flow controllers 201, 202,203, 207, 208, 209 can also be adjusted manually or by some otherautomated means to maintain the mercury concentration in exhaust stream35 within desired limits, according to control algorithms well known inthe art.

Referring still to FIG. 3A, there are illustrated several embodimentsfor preparation and injection of carbon nanocomposite sorbents, promotedcarbon sorbents, halogen and halide promoters, and/or alkali components.Stream 111 provides for introduction of carbon nanocomposite sorbentfrom reservoir 110, as metered by flow controller 201 manually or underthe direction of computer 206. The halogen/halide can be combined andreact with the carbon nanocomposite sorbent according to any of severalprovided methods. The halogen/halide (120 and/or 130) can be combinedvia transport line 121 (and/or 131) directly into transport line 115 (or113), within which it contacts and reacts with the carbon nanocompositesorbent (e.g., in reservoir 110) prior to injection point 116 (or 114).This option is one form of what is referred to herein as “in-flight”preparation of a promoted carbon sorbent in accordance with theinvention. Further, the halogen/halide (120 and/or 130) can be combinedvia flue gas stream 15 by transport line 121 (and/or 131) into transportline 115 and injection point 116 which it contacts and reacts with thecarbon nanocomposite (e.g., from reservoir 110) in flue gas stream 15after the carbon nanocomposite is transported in transport line 113 andinjected at injection point 114. This option is another form of what isreferred to herein as “in-flight” preparation of a promoted carbonnanocomposite sorbent in accordance with the invention. Further, thehalogen/halide can be combined via transport line 121 b with carbonnanocomposite sorbent prior to entering transport line 113 and/or 115.Still further, the halogen/halide can be contacted and react with thecarbon nanocomposite sorbent by introduction via transport line 121 cinto reservoir 110. This option can be employed when, for example,reservoir 110 includes an ebulliated or fluidized bed of carbonnanocomposite sorbent, through which halogen/halide flows in gaseousform or as a vapor. In other embodiments, the halogen/halide can becontacted with the carbon nanocomposite sorbent in liquid form or in asolvent, as discussed previously, and solvent removal (not shown in FIG.3A) can then be provided if necessary as mentioned with respect toembodiments discussed with reference to FIG. 1.

Similarly, the optional secondary component can be contacted and reactdirectly in transport line 115 (and/or 113) via transport line 131, oroptionally as described above with respect to the halogen/halide, viatransport lines 131 b and 131 c.

Similarly, the optional alkali component from reservoir 180 can eitherbe added in transport line 113 and/or 115 directly, or can be injectedseparately by transport line 118, remaining separate and/or combiningdownstream in flue gas stream 15 for synergistic effects with carbonnanocomposite sorbent, promoted carbon, or optional secondarycomponents. On-site variation of the amount of the optional alkalicomponent relative to carbon nanocomposite sorbent, promoted carbon, oroptional secondary components can be optimized for site-specificoperating and flue gas conditions.

FIG. 3B shows a schematic flow diagram of mercury control system 300including preparation of promoted carbon sorbents and flue gas mercuryreduction in accordance with embodiments of the present invention.Carbon sorbent 310 can be injected through line 395 to location 396 orinjected through line 390 to location 391. Promoted carbon sorbent 320can be injected through line 395 to location 396 or injected throughline 390 to location 391. Carbon sorbent 310 can be promoted in-flight,such as via injection of carbon sorbent 310 through line 390 and/or 395to location 391 and/or 396 with halogen/halide promoter 340 through line380 to location 385 or via injection of carbon sorbent 310 through line390 and/or 395 to location 391 and/or 396 with halogen/halide promoter340 through line 350 to location 355 and/or halogen/halide promoter 340through line 360 to location 365 and/or halogen/halide promoter 340through line 370 to location 375.

In addition to or as an alternative to use of promoted carbonnanocomposite prior to the optional ESP unit, the optional scrubber unitcan be used for removal of pollutants such as mercury via use ofpromoted carbon in the scrubber, removal of pollutants such as SO₂ viause of basic aqueous solution in the scrubber, removal of particulatesin the scrubber, or any combination thereof. Injection of materials suchas promoter or carbon nanocomposite sorbent to the scrubber can occur inthe scrubber or between the ESP and the scrubber. Promoted sorbent 320can be injected through line 397 into the scrubber. Carbon sorbent 310can be promoted in-flight, such as via injection of carbon sorbent 310through a heated carrier line (not shown) with promoter 340 to thescrubber. Halogen/halide promoter 340 can be added to the scrubberthrough line 381, while carbon sorbent 310 is added via line 397, andthe sorbent can be promoted within the scrubber.

In some embodiments wherein contacting between components and reactionis performed in a liquid or solvent phase, stirring of such liquidand/or slurry mixtures can be provided. In some embodiments, thehalogen/halide promoter and optional secondary component(s) can besprayed in solution form into or on the carbon nanocomposite sorbent. Insome such embodiments, drying, filtering, centrifugation, settling,decantation, or other solvent removal methods as are known in the artcan then be provided.

In embodiments wherein the halogen/halide promoter is in gaseous orvapor form, it can be diluted in air, nitrogen, or other gas asappropriate. The halide/halogen gas, for example, gaseous HBr or Br₂,can be passed through an ebulliated or fluidized bed of granular orfibrous carbon nanocomposite sorbent, with the promoted carbon sorbentso produced removed from the top of the bed via gas entrainment forinjection.

In some embodiments, the secondary component(s) can include iodine orother halogens, hydrohalides, including without limitation HI, HBr, HCl,a Group V or Group VI element with a molecular halogen, such as SCl₂ andothers. In some embodiments, the promoted carbon sorbent can includefrom about 1 g to about 30 g halogen/halide per 100 g carbonnanocomposite sorbent. In some embodiments, the promoted carbon sorbentcan include a secondary component in concentration of from about 1 wt %to about 15 wt % of the concentration of the halogen/halide component.

In still other embodiments, the promoted carbon nanocomposite sorbentcan be applied to a substrate. In other embodiments, such preparedsubstrate(s) can be caused to contact a polluted flue gas orgasification system product gas stream for mercury reduction purposes.Such substrates can be monolithic, rotating, moving, or exposed to thegas stream in any number of ways known to those skilled in the art.Substrates can include, for example, honeycomb structures, fabrics,filters, plates, and the like.

EXAMPLES

The present invention can be better understood by reference to thefollowing examples which are offered by way of illustration. The presentinvention is not limited to the examples given herein.

Example 1 Mesoporous Activated Carbon (AC) Nanocomposites fromCommercial Cane Molasses Example 1.1 NanoG-CM

High-surface-area montmorillonite (clay) obtained from Aldrich (200 g)was added rapidly to Brer Rabbit molasses (nonsulfurated) diluted with asmaller amount of water (200 g/140 mL) and stirred to make a thickpaste.

As soon as all the clay was wetted with the molasses, the paste wasdried overnight at 110° C. to remove excess water. Alternatively, asmaller portion of the paste was heated for 1 min in a microwave. Asmaller batch was dried more quickly (1 hour) in the oven at 110° C.

The dried solid was loaded in two batches in a cylindrical steel tubeand heated to 700° C. in a tube furnace with a flow of nitrogen throughthe bed. The effluent gas was bubbled through a water trap. Heating wascontinued for 1 hour.

The tube was cooled slowly to ambient under nitrogen and emptied. Theresulting black chunks of composite carbon were weighed and ground in amortar and pestle. The product nanocomposite was separated into twosieve sizes, greater than 325 mesh and about 325 mesh. The about 325mesh material was used for the Hg capture tests.

Yield of nanocomposite was 217 g.

Example 1.2 NanoG-CB

Preparation was similar to NanoG-CM, except high-sodium bentonite wassubstituted for the montmorillonite. Yield was 10.1 g from 10.0 grams ofbentonite.

Example 1.3 Impregnation of Promotion Agent Example 1.3.1 AmmoniumBromide

An aqueous solution of ammonium bromide (7.3 g/35 mL) was added to 54 gof 325-mesh nanocomposite and stirred to form a paste. The paste wasdried at 110° C. and reground.

Example 1.3.2 Hydrogen Bromide

Aqueous HBr (0.1 N) was added to NanoG-CM (10 g) and the mixture stirredfor 1 hr. The slurry was filtered and dried at 110° C.

Example 1.3.3 Bromine

Bromine vapor (0.5 g) was transferred to a vial containing the powderedcomposite (10 g), where it was adsorbed.

Example 1.3.4 Sulfur

Elemental sulfur (1 g) was dissolved in carbon disulfide (20 mL), and 10g of NanoG-CM was added. After being stirred overnight, the carbondisulfide was removed.

Example 2 Mesoporous Activated Carbon Nanocomposites from AmericanCrystal Sugar (ACS) Raffinate

The previous versions of the NanoG-CM carbon composites were preparedusing cane sugar molasses. Using the local ACS molasses would provide amore convenient source; e.g., a low-value raffinate remaining from sugarand betaine extraction is available in large amounts (approximately 170tons). However, the amount of dissolved inorganic salts is much higher(>10%) than commercial cane molasses, and the sugar content is lower.

Nanocomposites were prepared using the ACS raffinate and two types ofclay: a highly swelling, high-sodium bentonite and a low-swellingmontmorillonite from Aldrich. Both were ground finely.

Example 2.1 NanoG-ACSB

The bentonite was swelled by adding 10 g of dry bentonite to 80 g ofwater and grinding with a mortar and pestle. ACS raffinate (10 g) wasadded to the gelled mixture and mixed by grinding. After standingovernight to further disperse the sugar in the raffinate into the clay,the mixture was heated in a microwave at full power for 1 minute todevelop macroporosity in the gel. The gel was dried overnight in adrying oven at 110° C.

The dried solid was loaded in two batches in a cylindrical steel tubeand heated to 700° C. in a tube furnace with a flow of nitrogen throughthe bed. The effluent gas was bubbled through a water trap. Heating wascontinued for 1 hr. The tube was cooled slowly to ambient under nitrogenand emptied. The resulting black chunks of composite carbon were weighedand ground in a mortar and pestle.

Yield of nanocomposite was 10.2 g.

Example 2.2 NanoG-2ACSB

Preparation was similar to NanoG-ACSB except the weight of raffinateadded was doubled. Yield was 10.5 g.

Example 2.3 NanoG-2ACSM

Preparation was similar to NanoG-CM, using 10 g of Aldrichmontmorillonite and 20 g of ACS raffinate was used and the amountdoubled. Yield was 10.5 g.

Example 2.4 NanoG-2ACSB—Washed

A sample of NanoG-2ACSB was stirred with water overnight, filtered, andthen stirred with 0.1 N HBr for 2 hr. The slurry was filtered, and thecomposite was dried at 110° C.

Example 2.5 Impregnation of Promotion Agent Example 2.5.1 AmmoniumBromide

An aqueous solution of ammonium bromide (1.1 g/5 mL) was added to 10 gof nanocomposite and stirred to form a paste. The paste was dried at110° C. and reground.

Example 2.5.2 Bromine

Bromine vapor (0.5 g) was transferred to a vial containing the powderedcomposite, where it was partially adsorbed (chemisorbed).

Example 3 Bench-Scale Hg Sorption Tests of NanoG Sorbents

Bench-scale Hg sorption tests were conducted to evaluate the performanceof the sorbents in a bed configuration for sorption of elemental Hgvapor in flue gas. These results are summarized in Table 1. While not asaccurate at evaluating performance in an injection mode with very shortcontact time, the initial reactivity (as % Hg capture) and the initialslope gave a preliminary determination of reactivity in a short timescale. When the initial slope is flat, there are many active sites, anda higher reactivity has been found. A steep initial slope relates tofast breakthrough and corresponding lower reactivity.

The NanoG composite sorbents prepared from the cane molasses (NanoG-CM)gave excellent reactivities (98%-99% capture) at the start of theexperiment and continued with high capture efficiency for 15 minutes(flat slope). On the other hand, the ACS raffinate gave lowerreactivities and lower capacities (shorter 50% breakthrough times)compared with the composites prepared from cane sugar molasses. Theamounts of carbon contained in the ACS composites were considerablyless, owing to the lower sugar content, higher salt content and,perhaps, different burn-off rate. The composites prepared with doublethe amount of molasses were less reactive than the lower dosage. Theseresults could be explained by salt blockage in the pores of thecomposites from the ACS raffinate. The evolution of large amounts of H₂Swhen water was added to the sorbents is consistent with the formation ofK₂S in the pores resulting from reduction of sulfate as well as the highpotassium concentration. When the ACS raffinate sorbent was washed todissolve out the salts, the reactivity and capacity improvedconsiderably.

TABLE 1 Summary Results for Fixed-Bed Screening of NanoG SorbentsInitial 50% Promotion Reactivity, Initial Breakthrough, Sorbent Reagent% Hg Capture slope Time, hr NanoG-CM Br₂ 98 Flat 0.45 NanoG-CM NH₄Br 99Flat 0.38 NanoG-CM HBr 97 Moderate 0.29 NanoG-CM S 92 Steep 0.06 NanoG-Br₂ 67 Steep 0.02 2ACSM NanoG-2ACSB Br₂ 95 Steep 0.16 NanoG-2ACSB NH₄Br90 Steep 0.29 NanoG-ACSB NH₄Br 97 Moderate 0.32 NanoG- Br₂ 97 Moderate0.53 2ACSB- washed

Although sulfurization of ACs produces carbons with good reactivitiesfor Hg, the addition of sulfur to the NanoG sorbent did not result in agood capacity. It is likely that the sulfur blocked the pores in thelimited amount of carbon porosity available in these sorbents.

A comparison of HBr with Br₂ showed that Br₂ gave higher reactivity andcapacity. A reason for this may be that carbenium-bromide ion pairs inthese composite sorbents are less hydrated and more reactive in thesorbents produced by vapor deposition.

The ammonium bromide-promoted sorbents gave very good reactivities andcapacities, consistent with decomposition of the ammonium bromide in thepores on heating forming ammonia and gaseous HBr. The HBr combines withcarbon deposited on the proximate nanocarbon surfaces decorating theclay layers (sheets). Also, the ammonia is trapped inside the acidicclay layers of the composite where it is available for intercepting theSO₂ in the flue gas before it can oxidize on the carbon surface.

Example 4 Pilot-Scale Evaluation

NanoG-CM was evaluated at the pilot scale during a Center for Air ToxicMetals® (CATM®)-sponsored run of the particulate test combustor (PTC).The coal for that evaluation was a subbituminous Montana Powder RiverBasin (PRB) (Absaloka), and comparisons were made to a commerciallyavailable untreated carbon.

Results from the PTC tests are summarized in FIG. 4 for the commerciallyavailable standard AC and two options with NanoG-CM. FIG. 4 shows PTCresults for NanoG-CM testing on a total-injected-sorbent basis. Thestandard AC and the untreated NanoG-CM were tested with the moderateenergy dissociation technology (MEDT) sorbent enhancement additive (SEA)option. As indicated in the figure, the results were better with thestandard AC; however, the NanoG-CM did show potential for in-flightcapture. More promising results were obtained with a treated sample ofNanoG-CM. It was determined through a set of tests performed for MEDTSEA development that the pretreatment used with NanoG-CM was mosteffective at pre-air heater temperatures. Therefore, during evaluationof the treated NanoG-CM, it was injected into the ductwork at a pointwhere the flue gas temperature was approximately 715° F.

FIG. 4 suggests that the NanoG-CM material shows potential as anin-flight mercury sorbent, but the total injected sorbent rates arehigher than those with the standard AC. However, an alternate comparisonis to evaluate the test results on a carbon component basis, since theunderlying economic assumption for composite sorbents is that the ACcomponent is perhaps an order of magnitude more expensive than theinorganic substrate. The results from FIG. 4 have been rescaled in FIG.5 to depict the equivalent carbon-only injection rate for the threeoptions. FIG. 5 shows PTC results for NanoG-CM testing on acarbon-component basis. The standard AC results remain unchanged becausethey were considered 100% AC (mineral components of the carbon were notdeducted), but the NanoG-CM data reflect much lower carbon-onlyinjection rates since the average carbon content for NanoG-CM was only8%.

The carbon-only results of FIG. 5 demonstrate at least one of thebeneficial aspects of the nanocomposite sorbents: increased carbonutilization. Comparison of the standard AC and the NanoG-CM results inFIG. 5 suggests that the bulk of the standard AC's carbon content (e.g.,the interior portion) goes unused and is not a factor in overall mercurycapture. This reinforces a mechanistic understanding that predominantlythe surface and near-surface sites are important for in-flight captureof mercury. Improved carbon utilization can have a beneficial effect onconsumable sorbent cost, for example, if the base material costadvantage is not outweighed by added or more complicated productionsteps. Furthermore, improved carbon utilization can make it easier forutilities to meet carbon content restrictions in fly ash, for example,in fly ash destined for use in concrete.

Synergistic effects between the carbon layer and the interior substratecan be an advantage of the carbon nanocomposite sorbent. In one example,a synergistic effect could arise from a single particle including twosorbents: a conventional AC and an inorganic substrate that may bereactive toward acid gas components in flue gas. To support thepotential benefits of a nanocomposite sorbent, an applied model forin-flight capture was used with results presented in FIG. 6, forcomposite sorbents with varying activated carbon surface coverage. FIG.6 shows model results for in-flight mercury capture with a compositesorbent in a high-sulfur flue gas (3000 ppm SO₂, 15 ppm SO₃). Themodeled flue gas was representative of a high-sulfur coal withsignificant amounts of SO₃ that limit mercury capture, as indicated bythe 100% AC reference curve. An estimate of the synergistic benefit ofthe composite sorbent is shown by the 50% and 10% AC curves. Given theconservative assumptions that were used, benefits can exceed those shownby the model.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention that in theuse of such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments and optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in the artand that such modifications and variations are considered to be withinthe scope of this invention as defined by the appended claims.

Additional Embodiments

The present invention provides for the following exemplary embodiments,the numbering of which is not to be construed as designating levels ofimportance:

Embodiment 1 provides a method for separating a material from a gas thatincludes the material, including providing or obtaining a carbonnanocomposite sorbent; contacting at least some of the material with thesorbent, to form a material-sorbent composition; and separating at leastsome of the material-sorbent composition from the material-containinggas, to give a separated gas.

Embodiment 2 provides the method of Embodiment 1, wherein the materialis a pollutant.

Embodiment 3 provides the method of Embodiment 2, wherein the pollutantis mercury.

Embodiment 4 provides the method of any one of Embodiments 2-3, furtherincluding providing a promoter; and promoting at least a portion of thesorbent material by chemically reacting the portion of the sorbentmaterial with the promoter to form a promoted sorbent; wherein thesorbent that contacts at least some of the pollutant includes thepromoted sorbent.

Embodiment 5 provides the method of Embodiment 4, wherein the promoteris a halogen or halide promoter.

Embodiment 6 provides a method for reducing the pollutant content of apollutant-containing gas, including providing or obtaining a carbonnanocomposite sorbent material; providing or obtaining a halogen orhalide promoter; promoting at least a portion of the sorbent material bychemically reacting the portion of the sorbent material with the halogenor halide promoter to form a promoted sorbent; contacting at least partof the promoted sorbent with the pollutant in the pollutant-containinggas, to form a pollutant-sorbent composition; and separatingparticulates from the pollutant-containing gas, the particulatesincluding at least some of the pollutant-sorbent composition, to give acleaned gas.

Embodiment 7 provides the method of Embodiment 6, wherein the pollutantis mercury.

Embodiment 8 provides the method of any one of Embodiments 6-7, whereinobtaining or providing the carbon nanocomposite sorbent includesproviding or obtaining a carbon precursor; providing or obtaining asubstrate material; contacting the carbon precursor and the substratematerial, to provide a nanocomposite starting material; heating thenanocomposite starting material, to provide the carbon nanocompositesorbent.

Embodiment 9 provides the method of Embodiment 8, further includingallowing the heated nanocomposite starting material to react with anacid or a base, to provide the carbon nanocomposite sorbent.

Embodiment 10 provides the method of any one of Embodiments 8-9, whereinthe carbon precursor includes a carbohydrate.

Embodiment 11 provides the method of any one of Embodiments 8-10,wherein the carbon precursor includes brown sugar, barley sugar,caramel, cane sugar, corn syrup, starch, molasses, or a sugar wasteproduct.

Embodiment 12 provides the method of any one of Embodiments 8-11,wherein the substrate material includes diatomaceous earth, clay,zeolite, or mineral.

Embodiment 13 provides the method of any one of Embodiments 8-12,wherein the heating includes heating to greater than about 100° C.

Embodiment 14 provides the method of any one of Embodiments 6-13,wherein the sorbent material includes binding sites that bind with thepollutant in the pollutant-containing gas.

Embodiment 15 provides the method of any one of Embodiments 6-14,wherein the sorbent material includes carbon that has been allowed toreact or become impregnated with halogens, hydrogen halides, and Group Vand Group VI halides to form pollutant binding sites in the promotedsorbent.

Embodiment 16 provides the method of Embodiment 15, wherein the bindingsites in the promoted AC bind to the pollutant in thepollutant-containing gas to form the pollutant-sorbent composition.

Embodiment 17 provides the method of any one of Embodiments 15-16,wherein the binding sites in the promoted AC react with the pollutant inthe pollutant-containing gas to form the pollutant-sorbent composition.

Embodiment 18 provides the method of any one of Embodiments 15-17,wherein at least a portion of the binding sites of the AC react withoxidized pollutant in the pollutant-containing gas to form anotherpollutant-sorbent chemical composition.

Embodiment 19 provides the method of any one of Embodiments 6-18,wherein the step of separating particulates from thepollutant-containing gas includes separating in a particulate separatorincluding one or more ESPs.

Embodiment 20 provides the method of any one of Embodiments 7-19,wherein the mercury in the mercury-containing gas includes elementalmercury.

Embodiment 21 provides the method of any one of Embodiments 7-20,wherein the mercury in the mercury-sorbent composition is oxidizedmercury.

Embodiment 22 provides the method of any one of Embodiments 7-21,wherein the promoted sorbent combines with at least about 70 wt % of themercury present in the mercury-containing gas.

Embodiment 23 provides the method of any one of Embodiments 6-22,wherein the halogen or halide promoter is in a form including a vaporform, a solid form, in a solvent, or a combination thereof.

Embodiment 24 provides the method of any one of Embodiments 6-23,wherein the halogen or halide promoter includes at least one of Group Vhalide, Group VI halide, or mixtures thereof.

Embodiment 25 provides the method of any one of Embodiments 6-24,wherein a promoter precursor on the sorbent or injected with the sorbenttransforms into the halogen or halide promoter that reacts with thesorbent.

Embodiment 26 provides the method of any one of Embodiments 6-25,wherein the halogen or halide promoter is NH₄Br, NaBr, HBr, NaCl, CaCl₂,or HCl.

Embodiment 27 provides the method of any one of Embodiments 6-26,further including injecting an alkaline component into thepollutant-containing gas.

Embodiment 28 provides the method of Embodiment 27, wherein the alkalinecomponent includes an oxide, hydroxide, carbonate, or phosphate of analkali or alkaline-earth element.

Embodiment 29 provides the method of any one of Embodiments 6-28,further including adding an additional halogen or halide promoter to thepromoted sorbent.

Embodiment 30 provides the method of Embodiment 29, wherein theadditional halogen or halide promoter includes HI, HBr, HCl, a Group Velement with halogen, or a Group VI element with halogen.

Embodiment 31 provides the method of any one of Embodiments 6-30,further including adding a stabilizing agent to the promoted containingsorbent.

Embodiment 32 provides the method of Embodiment 31, wherein thestabilizing agent includes at least one of S, Se, H₂S, SO₂, H₂Se, SeO₂,CS₂, P₂S₅, or mixtures thereof.

Embodiment 33 provides the method of any one of Embodiments 6-32,wherein the step of promoting at least a portion of the sorbent materialoccurs at least partially before the contacting of thepollutant-containing gas with the promoted sorbent.

Embodiment 34 provides the method of any one of Embodiments 6-33,further including injecting the carbon nanocomposite sorbent at aninjection rate and injecting separately at least one promoter at aninjection rate into a gas stream whereby in-flight reaction produces thepromoted sorbent, wherein the promoter is selected from the groupconsisting of molecular halogens, halides, and combinations thereof,wherein the promoter is reacted in the gas phase or as a vapor, whereinthe promoter is added at from about 1 to about 30 grams per about 100grams of carbon nanocomposite sorbent material.

Embodiment 35 provides the method of Embodiment 34, wherein the gasstream is the pollutant-containing gas.

Embodiment 36 provides the method according to Embodiment 35,

wherein the gas stream is a transport gas.

Embodiment 37 provides the method of any one of Embodiments 34-36,wherein the promoter injection rate and the sorbent injection rate intothe gas are determined, at least in part, from a monitored pollutantcontent of the cleaned gas.

Embodiment 38 provides the method of any one of Embodiments 6-37,further including a step of regenerating the promoted sorbent from thepollutant-sorbent chemical composition.

Embodiment 39 provides the method of Embodiment 38, further includingusing the regenerated promoted sorbent to remove the pollutant from thepollutant-containing gas.

Embodiment 40 provides the method of any one of Embodiments 6-39,wherein at least one of the promoting, the contacting, or theseparating, occurs in an aqueous scrubber.

Embodiment 41 provides the method of Embodiment 40, wherein thepromoting occurs in the scrubber, wherein the scrubber includes anaqueous slurry that includes the promoter.

Embodiment 42 provides the method of any one of Embodiments 40-41,wherein the contacting occurs in the scrubber, wherein the scrubberincludes an aqueous slurry that includes that activated carbonnanocomposite sorbent.

Embodiment 43 provides a method for reducing the mercury content of amercury-containing gas, including providing or obtaining a carbonnanocomposite sorbent, the carbon nanocomposite sorbent made by stepsincluding providing or obtaining a carbon precursor; providing orobtaining a substrate material; contacting the carbon precursor and thesubstrate material, to provide a nanocomposite starting material; andheating the nanocomposite starting material, provide the carbonnanocomposite sorbent; providing or obtaining a halogen or halidepromoter; promoting at least a portion of the sorbent material bychemically reacting the portion of the sorbent material with the halogenor halide promoter to form a promoted sorbent; contacting at least partof the promoted sorbent with the mercury, to form a mercury-sorbentcomposition; and separating at least some of the mercury-sorbentcomposition from the mercury-containing gas.

Embodiment 44 provides a method of making a carbon nanocompositesorbent, including providing or obtaining a carbon precursor; providingor obtaining a substrate material; contacting the carbon precursor andthe substrate material, to provide a nanocomposite starting material;heating the nanocomposite starting material, to provide the carbonnanocomposite sorbent.

Embodiment 45 provides the carbon nanocomposite sorbent made by themethod of Embodiment 44.

Embodiment 46 provides a promoted carbon nanocomposite sorbent made by amethod comprising promoting at least a portion of the sorbent materialof Embodiment 45 by chemically reacting the portion of the sorbentmaterial with a halogen or halide promoter to form the promoted sorbent.

Embodiment 47 provides a mercury-sorbent composition made by contactingthe carbon nanocomposite sorbent of any one of Embodiments 45-46 with amercury-containing gas.

Embodiment 48 provides the carbon nanocomposite sorbent of any one ofEmbodiments 45-47 in contact with mercury or oxidized mercury.

Embodiment 49 provides a promoted carbon nanocomposite sorbent made by amethod comprising promoting at least a portion of carbon nanocompositesorbent material by chemically reacting the portion of the sorbentmaterial with a halogen or halide promoter to form the promoted sorbent.

Embodiment 50 provides the apparatus or method of any one or anycombination of Embodiments 1-49 optionally configured such that allelements or options recited are available to use or select from.

We claim:
 1. A method for reducing the pollutant content of apollutant-containing gas, comprising: providing or obtaining a carbonnanocomposite sorbent material; providing or obtaining a halogen orhalide promoter; promoting at least a portion of the sorbent material bychemically reacting the portion of the sorbent material with the halogenor halide promoter to form a promoted sorbent; contacting at least partof the promoted sorbent with the pollutant, to form a pollutant-sorbentcomposition; and separating at least some of the pollutant-sorbentcomposition from the pollutant-containing gas, to give a cleaned gas. 2.The method of claim 1, wherein the pollutant is mercury.
 3. The methodof claim 1, wherein obtaining or providing the carbon nanocompositesorbent comprises: providing or obtaining a carbon precursor; providingor obtaining a substrate material; contacting the carbon precursor andthe substrate material, to provide a nanocomposite starting material;heating the nanocomposite starting material, to provide the carbonnanocomposite sorbent.
 4. The method of claim 3, wherein the carbonprecursor comprises a carbohydrate.
 5. The method of claim 3, whereinthe carbon precursor comprises brown sugar, barley sugar, caramel, canesugar, corn syrup, molasses, starch, or a sugar waste product.
 6. Themethod of claim 3, wherein the substrate material comprises diatomaceousearth, clay, zeolite, or mineral.
 7. The method of claim 1, whereinseparating at least some of the pollutant-sorbent composition from thepollutant-containing gas comprises separating particulates from thepollutant-containing gas, the particulates comprising at least some ofthe pollutant-sorbent composition.
 8. The method of claim 2, wherein thepromoted sorbent combines with at least about 70 wt % of the mercurypresent in the mercury-containing gas.
 9. The method of claim 1, whereinthe halogen or halide promoter is in a form comprising a vapor form, asolid form, in a solvent, or a combination thereof.
 10. The method ofclaim 1, wherein the halogen or halide promoter comprises at least oneof Group V halide, Group VI halide, or a mixture thereof.
 11. The methodof claim 1, wherein a promoter precursor transforms into the halogen orhalide promoter that reacts with the sorbent.
 12. The method of claim 1,wherein the halogen or halide promoter is NH₄Br, NaBr, CaBr₂, HBr, NaCl,CaCl₂, or HCl.
 13. The method of claim 1, wherein the contacting occursin a gas phase, a liquid phase, or a combination thereof.
 14. The methodof claim 1, wherein at least one of the promoting, the contacting, orthe separating, occurs in an aqueous scrubber.
 15. The method of claim14, wherein the promoting occurs in a scrubber, wherein the scrubberincludes an aqueous slurry that includes the promoter.
 16. The method ofclaim 1, wherein the contacting occurs in the scrubber, wherein thescrubber includes an aqueous slurry that includes that activated carbonnanocomposite sorbent.
 17. The method of claim 1, further comprisinginjecting the carbon nanocomposite sorbent material at an injection rateand injecting separately at least one promoter at an injection rate intoa gas stream whereby in-flight reaction produces the promoted sorbent,wherein the promoter is selected from the group consisting of molecularhalogens, halides, and combinations thereof, wherein the promoter isreacted in gas phase or as a vapor, wherein the promoter is added atfrom about 1 gram to about 30 grams per about 100 grams of carbonnanocomposite sorbent material.
 18. The method of claim 1, furthercomprising reducing the concentration of SO₂ or SO₃ in thepollutant-containing gas.
 19. A method for reducing the mercury contentof a mercury-containing gas, comprising: providing or obtaining a carbonnanocomposite sorbent, the carbon nanocomposite sorbent made by stepscomprising providing or obtaining a carbon precursor; providing orobtaining a substrate material; contacting the carbon precursor and thesubstrate material, to provide a nanocomposite starting material; andheating the nanocomposite starting material, to provide the carbonnanocomposite sorbent; providing or obtaining a halogen or halidepromoter; promoting at least a portion of the sorbent material bychemically reacting the portion of the sorbent material with the halogenor halide promoter to form a promoted sorbent; contacting at least partof the promoted sorbent with the mercury, to form a mercury-sorbentcomposition; and separating at least some of the mercury-sorbentcomposition from the pollutant-containing gas.
 20. A method of making acarbon nanocomposite sorbent, comprising: providing or obtaining acarbon precursor; providing or obtaining a substrate material;contacting the carbon precursor and the substrate material, to provide ananocomposite starting material; and heating the nanocomposite startingmaterial, to provide the carbon nanocomposite sorbent.
 21. The carbonnanocomposite sorbent made by the method of claim
 20. 22. A promotedcarbon nanocomposite sorbent made by a method comprising promoting atleast a portion of the carbon nanocomposite sorbent of claim 21 bychemically reacting the portion of the carbon nanocomposite sorbent witha halogen or halide promoter to form the promoted carbon nanocompositesorbent.